Beams used for buildings have been manufactured by various methods. For example, steel beams, pre-stressed concrete (PSC or PC) beams, or steel composite beams obtained by combining steel and concrete have been used.
FIG. 1 shows an example where an I-shaped steel beam 20 is installed between steel columns 10 at opposite ends thereof using splice beams 11, and then slab concrete 30 is cast and cured on the top of the I-shaped steel beam 20, which is considered as showing a most typical method of constructing a slab using a beam for a building.
However, since this I-shaped steel beam 20 is somewhat expensive, considering the high price of steel plate nowadays, it is rather uneconomical.
Particularly, in connection with a composite beam made by combination of steel and concrete, a sandwich composite beam 40 is shown in FIGS. 2 and 3.
The sandwich composite beam 40 of FIG. 2 is composed of lateral section-beams 41 spaced apart from each other in parallel and concrete 42 filled between the lateral section-beams 41. To cast the concrete 42, a lower support plate 43 placed on lower inner flanges of the lateral section-beams 41 is provided. The sandwich composite beam 40 of FIG. 3 is composed of the lateral section-beams 41 that are H-shaped steels spaced apart from each other in parallel, the concrete 42 filled between the lateral section-beams 41, tendons 44 buried in the concrete 42, and the lower support plate 43 placed on lower inner flanges of the lateral section-beams 41 in order to cast the concrete 42.
However, due to its excessive use of the section-beams 41 and a fire-proof covering, from an economic standpoint, this sandwich composite beam 40 is difficult to adopt. In a typical building, H-shaped steels are mainly used for framework. To connect the sandwich composite beam 40 with the H-shaped steel, some means of sufficiently securing connections between heterogeneous materials, i.e., between the steel of the H-shaped steel and the concrete of an end face of the sandwich composite beam, is required.
It is pointed out as a problem that this joining means inevitably reduces constructability, safety, and economy compared to a method of bolting a steel member (steel column) and another steel member (I-shaped steel beam) together as shown in FIG. 1. And, the dead weight of the composite beam is considerably increased because the concrete 42 fills the entire space between the section-beams 41.
Furthermore, since connecting numerous sandwich composite beams 40 to each other requires separate joining means, the connecting work also has a problem in that constructability is inevitably and severely reduced.
A different composite beam has been suggested, which has a honeycomb structure capable of installing pipe members including pipes for facilities on a web thereof. In the composite beam with the honeycomb structure, a steel sheath having an I-shaped cross section is manufactured, and its interior is filled with concrete. Here, web through-holes are formed in a web of the steel sheath. Thereby, the composite beam having the honeycomb structure has an advantage in that the pipe members including pipes for facilities can be installed in the through-holes. However, the composite beam having the honeycomb structure has a problem in that it requires a great deal of welding and somewhat complicated manufacturing, which also results in poor economic efficiency. When the composite beam having the honeycomb structure is installed between H-shaped steels, a joint between the steel of the H-shaped steel and the concrete of the end face of the composite beam also has a fundamental problem in that a separate joining means is required.